1. Field of the Invention
The present invention relates to an LED display apparatus and an LED displaying method capable of displaying color pictures of high quality by using a dot-matrix type LED display device having a relatively small number of dots and low resolution.
2. Description of Related Art
With the advent of LED (Light Emission Diode) capable of emitting blue light rays with high intensity or luminance, there have been developed in recent years full-color LED display devices or apparatus of a large size which can realize high visibility even in the open air. In practical applications, the full-color LED display apparatus began to be used for displaying pictures and information not only in sports fields and recreation grounds but also for outdoor and indoor advertisements.
For facilitating understanding of the concept underlying the invention, technical background thereof will first be described. FIG. 17 of the accompanying drawings is a block diagram showing a conventional LED display apparatus 1 known heretofore. Referring to the figure, a dot-matrix type LED display device or unit 2 includes a plurality of LEDs (8.times.8=64 LEDs in the device shown in FIG. 17) arrayed in the form of a dot matrix. A display data receiver 3 receives display data (i.e., data to be displayed) a from a display signal generation source such as a personal computer or the like (not shown) under the timing determined by a synchronizing signal b. A display data storage unit 4 serves for storing the display data a received by the display data receiver 3. On the other hand, the display data a stored in the display data storage unit 4 are read out by a display data read-out unit 5. A counter 8 counts a clock signal CK which provides a source for various timing signals. A comparison unit 9 compares the display data a read out from the display data read-out unit 5 with a count value outputted from the counter 8. A light emission driver control unit 10 outputs signals for controlling light emission driver circuits 11, 12 and 13 on the basis of an output signal of the comparison unit 9, wherein the light emission driver circuits 11, 12 and 13 drive relevant LEDs of the dot-matrix type LED display device 2, which will be described in more detail later on.
Next, description will be directed to the operations of the LED display apparatus 1 implemented in the structure described above. The display data a supplied from the display signal generation source are received by the display data receiver 3 under the timing given by the synchronizing signal b. The display data a as received are temporarily stored in the display data storage unit 4. The display data a stored in the display data storage unit 4 are read out by the display data read-out unit 5 under the timing of a timing signal t generated on the basis of the synchronizing signal b and supplied to the comparison unit 9 to be set therein.
On the other hand, the counter 8 starts to count the clock signal CK. The count value of the clock signal CK is compared with the display data a set at the comparison unit 9. In this conjunction, assume, only by way of example, that the number of the display data a set at the comparison unit 9 is "128". In that case, so long as the count value is smaller than "128" inclusive, the comparison unit 9 outputs a light emission enable signal (e.g. H-level signal) for enabling light emission of the LED. On the contrary, when the count value exceeds "128", the comparison unit 9 outputs a light emission inhibit signal (e.g. L-level signal) for disabling or inhibiting the light emission of the LED. In response to the output signal from the comparison unit 9, the light emission driver control unit 10 outputs a signal for controlling the light emission driver circuits 11, 12 and 13 for the relevant LEDs of the dot-matrix type LED display device 2.
In this manner, in the conventional LED display apparatus, the time for light emission of each of the LEDs is controlled on the basis of the display data a, which in turn means that display with gradation corresponding to the display data a can be realized. Thus, the LED display apparatus can generate not only character images but also motion picture images including various natural pictures. At this juncture, it should be mentioned that there are provided usually a plurality of comparison units 9 in correspondence to various LED blocks, although only one comparison unit 9 is shown. The same holds true in the following description as well.
However, when the conventional LED display apparatus is operated by using the personal computer as the display signal generation source for displaying on the dot-matrix type LED display device 2 the same contents as those displayed on the monitor of the personal computer, there arises a problem that difficulty is encountered in implementing such LED display apparatus at low cost, because an extremely large number of LEDs (e.g. 640.times.480 for each of red, blue and green displays in the case of color display) is required in order to meet the VGA (video graphics array) specifications for the personal computer.
This problem will be elucidated more concretely by taking as an example the display of character data by the conventional LED display apparatus. FIG. 18A of the accompanying drawings illustrates, only by way of example, display of an upper case alphabetic character "A" on the dot-matrix type LED display device 2 including an array of 16.times.16 dots. The display data a inputted from the display signal generation source such as the personal computer is composed of 16.times.16 dots on a frame-by-frame basis as illustrated in FIG. 18A, wherein each dot is represented by one red LED (R) (red light emission diode), one blue LED (B) and two green LEDs (G). In FIG. 18A, the dots designated by R, G and B each in a circle indicate that the corresponding LEDs are lit while the dots which are not labeled with R, G and B are not lit.
By contrast, FIG. 18B is a view for illustrating a corresponding image generated for the 16.times.16 display data inputted to the display data receiver 3 by processing the data such that 4 (2.times.2) dots are converted into one unit, whereon the four dot data contained in each of the units are averaged so as to constitute or represent one dot. The image shown in FIG. 18B is generated on the basis of the averaged data by selectively driving the relevant LEDs of the 8.times.8 dot-matrix type LED display device 2. From the comparison of the image shown in FIG. 18B with that of FIG. 18A, it can be seen that the image generated on the basis of the averaged display data shown in FIG. 18B is accompanied with rougher contours and thus remarkably degraded in respect to the resolution when compared with the image shown in FIG. 18A.
In the LED display apparatuses developed in recent years, it is demanded that color display of high quality or high definition should be able to be generated even with a dot-matrix type LED display unit composed of a small number of dots and exhibiting low resolution.